This invention relates generally to the field of devices used to secure metal tubing, and in particular thin-walled metal tubing, during end forming operations such as flaring, beading, upsizing and downsizing. More particularly, the invention relates to such devices which involve a clamping bar having one or more tube receiving bores, where the bar is divided into two members on a plane passing through the bore axis or axes, so that the bar halves may be separated for insertion of a metal tube into the bore. The two bar halves are then pressed together to tightly clamp the metal tube to prevent movement of the tube relative to the clamp in the axial direction.
There are numerous cold-forming operations which must be performed on relatively thin-walled metal tubes in order to provide a tube having a properly configured end segment for a particular application. Thin-walled tubes of aluminum, steel, or equivalent metals or alloys are well known and are used in thousands of different applications where a specific end configuration is required, such as to join the tubes to fittings or other components in an equipment fluid line. The tubes are created by taking a stock tube having a constant outer and inner diameter and altering the end of the tube by pressing a die onto the tube end in the axial direction, the die deforming the metal into the desired configuration. For example, the tube end may need to be flared into a conical or bell-shaped configuration, or an annular bead may need to be created about its circumference, or the tube end may need to be downsized or upsized. Because the force is applied in the axial direction, typically by a hydraulic press, and must be sufficient to deform the metal of the tube wall into the desired shape, the tube must be securely clamped to prevent movement of the tube in the axial direction. At the same time, because the tube is thin-walled, the clamping device must prevent any bending, folding or crimping during the cold forming operation.
A known clamping device for securing thin-walled metal tubes to prevent movement in the axial direction during cold forming operations comprises a base member and a removable clamping member, each having a mating surface having a substantially semi-circular channel cut therein, such that when the base and top members are joined the channels align to define a generally circular bore to receive the metal tube. A tube having an outer radius matching or slightly exceeding the channel radii is placed into the semi-circular channel of the base member with its end extending a short distance beyond the forward edge of the base member, and the semi-circular channel of the top member is positioned to encompass the tube. Force is then applied to the base and top member, thereby securely clamping the tube between the base and top members. The width of the base and top members in the axial direction must be sufficient to provide enough frictional resistance to secure the tube against the axial pressures encountered in the cold forming operation.
To improve the gripping ability of such clamps, it is known to provide the semi-circular channels with annular grooves in the plane perpendicular to the central axis by removing material to form V-shaped, U-shaped or rectilinearly walled grooves at spaced intervals along the main axis. When the top and base members are clamped together, the grooves allow the clamping device to grip the tube more securely than if the walls were smooth.
It is an object of this invention to provide for an improved clamping device for thin-walled metal tubes which precludes movement in the axial direction when cold forming pressure is applied against the tube end by providing annular grooves which are cold formed into the walls of the semi-circular channels rather being formed by a cutting or material-removing operation, such that each groove comprises a pair of raised shoulders which extend slightly out of the channel wall. The raised shoulders more securely grip the outer wall of the tube to create greater resistance to movement in the axial direction, allowing for a reduction in dimension for the clamp in the axial direction and allowing for application in the radial direction of a smaller clamping force against the tube itself. It is a further to provide such a clamping device wherein a simple cam mechanism is used to provide the clamping pressure so that the clamping operation can be performed easily and quickly without the need for securing and releasing threaded bolts. These and other objects not expressed in this section will be achieved by and apparent from the disclosure which follows.